The applicant has developed a number of suspension systems for multi-hulled water craft where the hulls are able to move relative to a chassis or body portion, examples of which are disclosed in U.S. Pat. No. 7,314,014, and international publication numbers WO 2011/143692 and WO 2011/143694, details of which are incorporated herein by reference.
While underway, in many situations there is little benefit to providing active heave motion compensation, i.e. precisely controlling the overall height of chassis or body portion. However while docked or otherwise engaging with another object, be it a fixed dock or floating pontoon or other vessel, it can be beneficial to provide active heave motion compensation or at least active compensation of the vertical height of a point or region on the vessel, such as the bow.
It is known to provide active adjustment of a platform to compensate for vertical motions in addition to roll and pitch motions as disclosed in U.S. Pat. No. 5,822,813. Servos are used to provide the force required to position and support the platform, the support being non-resilient. Therefore the support force must be exceeded to generate an extension of the servo, and so the higher the load being supported, the more energy is required to effect a given displacement adjustment.
In U.S. Pat. No. 9,073,605 the support of a platform above two hulls is resilient, with electromagnetic actuators being positioned in parallel with separate pneumatic support springs. The electro-magnetic actuators are used to provide a force to displace the platform in roll, pitch and heave, but a requirement for a continual force due to a manoeuvre, such as centrifugal force during turns or pitch forces due to longitudinal acceleration or deceleration requires continual supply of energy to the actuators to provide the continual force in parallel with the springs.
It is to be understood that the prior art publications discussed above does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.